[Qemu-devel] Re: [PATCH RFC] virtio: add features qdev property

[Gerd Hoffmann]

On 12/14/09 12:10, Michael S. Tsirkin wrote:
> On Mon, Dec 14, 2009 at 11:24:41AM +0100, Gerd Hoffmann wrote:
> for block:
>      if (strcmp(s->serial_str, "0"))
>          features |= 1<<  VIRTIO_BLK_F_IDENTIFY;
>
>      if (bdrv_is_read_only(s->bs))
>          features |= 1<<  VIRTIO_BLK_F_RO;

Sure you want these be configurable?

> Also, I'd like these things to be saved in bits and not add a ton
> of fields in device. Ideas how to do this?

I guess you only want disable features?

You could have a bitmap property then, which accepts names for the bits. 
 It would need a table like this ...

   char *bitnames[] = {
        [ VIRTIO_BLK_F_IDENTIFY ] = "blk-identify",
        [ VIRTIO_BLK_F_RO       [ = "blk-ro",
        [ ... ]
   };

Then the property parser would accepts strings such as 'bit1|bit2' and 
you can have

  -device 'virtio-blk-pci,disable=blk-identify|ring-indirect'

The driver will just do 'vdev->host_features &= ~disable'.

cheers,
  Gerd